Artificial expansile total lumbar and thoracic discs for posterior placement without supplemental instrumentation and its adaptation for anterior placement of artificial cervical, thoracic and lumbar discs

ABSTRACT

A total artificial expansible disc having at least two pairs of substantially parallel shells, which move in multiple directions defined by at least two axes, is disclosed. Several methods for implanting the total artificial expansile disc are also disclosed. The total artificial expansile disc occupies a space defined by a pair of vertebral endplates. An expansion device, which preferably includes a jackscrew mechanism, moves the pairs of shells in multiple directions. A core is disposed between the pairs of shells, and the core permits the vertebral endplates to move relative to one another.

This application is continuation-In-Part of copending application Ser.No. 10/964,633, filed on Oct. 15, 2004, which claims the benefit underTitle 35, U.S.C. §119 (e) of U.S. provisional application 60/578,319filed on Jun. 10, 2004; 60/573,346 filed on May 24, 2004; 60/572,468filed on May 20, 2004; 60/570,837 filed on May 14, 2004; and 60/570,098filed on May 12, 2004, the entire contents of which are herebyincorporated by reference and for which priority is claimed under 35U.S.C. § 120.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to artificial discs, and more specificallyrelates to artificial expansile total lumbar and thoracic discs forposterior placement without supplemental instrumentation, and toanterior placement of artificial discs for the cervical, thoracic andlumbar spine.

2. Description of the Relevant Art

Cervical and lumbar total artificial discs are entering the clinicalneurosurgical and orthopedic markets. The benefits of these artificialdiscs are well known. They replace diseased discs, and preserve motionsegment mobility. Discogenic and radicular pain are relieved withoutforfeiting segmental mobility, which is typical of traditional anterioror posterior lumbar fusions. Total artificial disc replacements aim tocover the entire expanse of the disc space because restoration of rangeof motion is reportedly greatest when roughly 80% of the vertebralendplate is covered. Thus it is only rational, currently to placeprosthetic discs anteriorly where access can be easily obtained, andthey can be secured by a variety of anterior screw fixations. Thistechnology is adequate for single level disc replacement in the cervicalspine. However based on the current anterior cervical prosthetic discscrew fixation methodology its implantation is periodically complicatedby screw failures e.g. partial or complete screw pullouts or breaks, andin most designs it is limited to single level replacement. Furthermore,for lumbar total artificial discs, placement is limited to only the L4/5and L5/S1 disc spaces, and not above, secondary to aortic and vena cavalanatomical restraints. Likewise, for the thoracic spine. Thus far notype of thoracic prosthetic disc device has been reported or described.Furthermore, despite the purported safety of placement of the currenttotal lumbar artificial discs, there is a significant risk of retrogradeejaculations in males, and the risk of vascular injury, which althoughsmall, is potentially catastrophic if it occurs.

The design of total artificial discs, which began in the 1970's, and inearnest in the 1980's, consists essentially of a core (synthetic nucleuspulposus) surrounded by a container (pseudo-annulus). Cores haveconsisted of rubber (polyolefin), polyurethane (Bryan-Cervical),silicon, stainless steel, metal on metal, ball on trough design(Bristol-Cervical, Prestige-Cervical), Ultra High Molecular WeightPolyethylene (UHMWPE) with either a biconvex design allowingunconstrained kinematic motion (Link SB Charite-Lumbar), or a monoconvexdesign allowing semiconstrained motion (Prodisc-Lumbar). There is also abiologic 3-D fabric artificial disc interwoven with high molecularweight polyethylene fiber, which has only been tested in animals.Cervical and lumbar artificial discs are premised on either mechanicalor viscoelastic design principles. The advantages of mechanical metal onmetal designs including the stainless steel ball on trough design andthe UHMWPE prostheses include their low friction, and excellent wearcharacteristics allowing long term motion preservation. Their majorlimitation is the lack of elasticity and shock absorption capacity. Thefavorable features of the viscoelastic prosthetics include unconstrainedkinematic motion with flexion, extension, lateral bending, axialrotation and translation, as well as its cushioning and shock absorptioncapacity. On the other hand, their long term durability beyond ten yearsis not currently known. Containers have consisted of titanium plates,cobalt chrome or bioactive materials. This history is reviewed and welldocumented in Guyer, R. D., and Ohnmeiss, D. D. “Intervertebral discprostheses”, Spine 28, Number 15S, S15-S23, 2003; and Wai, E. K.,Selmon, G. P. K. and Fraser, R. D. “Disc replacement arthroplasties: Canthe success of hip and knee replacements be repeated in the spine?”,Seminars in Spine Surgery 15, No 4: 473-482, 2003.

It would be ideal if total lumbar artificial discs could be placedposteriorly allowing access to all levels of the lumbar spine. Also onecould place these devices posteriorly in thoracic disc spaces through atranspedicular approach. Similarly if these devices can be placedanteriorly particularly in the cervical spine without anterior screwfixation, and custom-fit it for each disc in each individual, the easeof placement would reduce morbidity and allow for multi-level discreplacement. Placement of an artificial disc in the lumbar spine ifinserted posteriorly through a unilateral laminotomy by using aclassical open microscopic approach or by using a minimally invasivetubular endoscopic approach would significantly reduce the possibilityof recurrent disc herniation. If placed without facet joint violation,or with only unilateral mesial facetectomy, and the device can purchasethe endplates with spikes there would be no need for supplementalposterior pedicle screw fixation, thus obviating the associatedmorbidity associated with pedicle screws and bone harvesting. To take itone step further, if artificial lumbar discs can be posteriorly placedsuccessfully and safely throughout the entire lumbar spine, everyroutine lumbar discectomy could be augmented by artificial discplacement which would simultaneously eliminate discogenic and radicularpain while preserving flexibility. Furthermore by so doing, theprobability of recurrent herniation plummets, and subsequently the needfor posterior pedicle instrumentation plummets, thereby diminishingoverall spinal morbidity, expenditure, and leading to the overallimprovement in the quality of life.

Presumably up to now, technology is not focusing on posterior placementof total lumbar prosthetic discs because of inadequate access to thedisc space posteriorly. To circumvent this problem others have beenworking on the posterior placement, not of a total prosthetic disc butof a prosthetic disc nucleus (PDN), or essentially a core without acontainer (pseudo annulus). PDNs, which are considered post-discectomyaugmentations, have consisted of one of the following materials: 1)hydrogel core surrounded by a polyethylene jacket (Prosthetic DiscNucleus). Two of these devices have to be put in. There is a very high,38% extrusion rate, 2) Polyvinyl alcohol (Aquarelle), 3) polycarbonateurethane elastomer with a memory coiling spiral (Newcleus), 4) Hydrogelmemory coiling material that hydrates to fill then disc space, 5)Biodisc consisting of in-situ injectable and rapidly curable proteinhydrogel, 6) Prosthetic Intervertebral Nucleus (PIN) consisting of apolyurethane balloon implant with in-situ injectable rapidly curablepolyurethane and 7) thermopolymer nucleus implant. (See the twopublications identified above). The approach of posteriorly placingartificial disc cores appears to be flawed in that: 1) there is a highextrusion rate, 2) it lacks good fixation as does total prostheticdevices that are placed anteriorly, 3) it is restricted only to earlysymptomatically disrupted discs which have only nucleus pulposus but notannulus or endplate pathology, and 4) are contraindicated in discs withan interspace height of less than 5 mm.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a cross-section of the, expansile totallumbar/thoracic implant upon initial posterior insertion into the lumbar(or thoracic) disc space against the background of a vertebral body,i.e., this illustrates a three-dimensional expandable elastic polymernucleus design (Embodiment I);

FIG. 2 illustrates ratcheting of the three-dimensional expansile totallumbar/thoracic titanium shells to conform to the length of thevertebral body (Embodiment I);

FIG. 3 illustrates the dorsal view of the three-dimensional expansiletotal lumbar/thoracic construct from the surgeon's perspective(Embodiment I);

FIGS. 4A-M illustrate in detail the mechanical cylinder-spur-gear-spring(CSGS) system incorporated into the cross-connecting 8 titanium shellsof the three-dimensional Lumbar/Thoracic prosthesis which enableexpansion of the device in x, y and z dimensions. A system of springs isincorporated into the y-axis of the CSGS so as not to hinder theflexibility of the inner core.

FIGS. 5A and 5B illustrate a second embodiment of the three-dimensionalexpansile lumbar/thoracic disc invention, i.e., these illustrate anin-situ injection/expansion elastic polymer nucleus design (EmbodimentII);

FIGS. 6A, 6B and 6C illustrate a third embodiment of the expansile totallumbar/thoracic artificial disc implant, i.e., this illustrates amechanical metal on metal, stainless steel, ball on trough design(Embodiment III);

FIGS. 7A, 7B and 7C illustrate a fourth embodiment of thethree-dimensional expansile total lumbar/thoracic artificial discimplant, i.e., this illustrates a mechanical metal on metal, biconvexultra high molecular weight polyethylene (UHMWPE) design (EmbodimentIV);

FIG. 8 illustrates a fifth embodiment of the three-dimensional expansiletotal lumbar/thoracic artificial disc implant, i.e., this illustrates amechanical metal on metal, monoconvex UHMWPE design (Embodiment V);

FIGS. 9A-E illustrate a sixth embodiment of the expansile totallumbar/thoracic artificial disc implant. This simpler design expands intwo not three dimensions (height and width). The mechanism of expansionis based on calibrated ratcheting of corrugated interconnected bars.FIGS. 9A-E therefore represent a two-dimensional expansile prosthesis,using the elastic polymer nuclear design as the prototype (EmbodimentVI);

FIGS. 10A-E illustrate a seventh embodiment of the expansile totallumbar/thoracic artificial disc implant which expands in two dimensionsusing a jackscrew width expansion mechanism and a fixed-screw heightexpansion mechanism (Embodiment VII).

FIGS. 11A-D illustrate the precise mechanism of the jackscrew openingand closing employed in embodiment VII. The figures illustrate fourtypes of mechanisms; mechanical using a screw, electrical-wired control,electrical-wireless control, and a hybrid mechanical-electricalmechanism combining a screw and wired control.

FIG. 12A represents an endoscope variant of the present inventioninserted unilaterally into the disc space to inspect the disc spacecircumferentially;

FIG. 12B represents a specifically designed pituitary rongeur endoscopicattachment with a light source emanating from the junction of theadjoining dorsal and ventral cup forceps. This significantly aids inperforming a complete circumferential discectomy necessary for adequateprosthesis implantation.

FIG. 12C illustrates a right-angled ratchet driver integrated into anendoscope to assist in visualization of screws beneath the caudal aspectof the spinal cord or thecal sac, if necessary.

FIGS. 13A, 13B, 13C and 13D illustrate a cross-section of the prosthesesadapted for anterior implantation into the cervical disk space. FIG. 13Aillustrates the expandable elastic polymer nucleus design (EmbodimentI). FIG. 13B illustrates the in-situ injection/expansion elastic polymernucleus design (Embodiment II). FIG. 13C illustrates the mechanical,metal on metal, stainless steel, ball on trough design (Embodiment II).FIG. 13D illustrates the mechanical, metal on metal, UHMWPE biconvex ormonoconvex design (Embodiments IV and V).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The Medical Device

Referring now to FIGS. 1-4, the above described problem can be solved inthe lumbar/thoracic spine by the insertion of a total boomerang (bean)shaped prosthetic disc 100 including an expansile disc core 101surrounded by ratchetable titanium shells (containers) Q1-Q8 that canexpand geometrically in all three x, y, and z planes, horizontally,vertically and width wise.

The outer titanium shells Q1-Q8 themselves when ratcheted width-wisehave titanium spikes 103 inserting themselves into and purchasing theendplates, thus securing permanent integration into the vertebralendplates. The outer shell titanium surfaces can be treated withhydroxyappetite to facilitate bone incorporation. There is currentlyavailable a vertebral ratcheting corpectomy construct which can beratcheted up vertically until it purchases the rostral and caudalendplates with spikes. There are currently transpedicular/posteriorlumbar interbody fusion (T/PLIF) bean shaped constructs, which can beunilaterally inserted into disc spaces. There are currently static totalartificial discs (anteriorly placed). The present invention, however,constructs an expansile disc core within a boomerang (bean) shapedtitanium construct which can be unilaterally inserted posteriorly intothe lumbar and thoracic disc spaces, and can then be ratcheted invertical and horizontal dimensions to custom fit the implant with theheight and length of the individual vertebral body, and ratcheted widthwise to conform to the individual width of the a disc space. This totalprosthetic device can be secured to the endplates with spike attachments(teeth).

FIG. 1 illustrates a cross-section of the implant 100 upon initialposterior insertion into the lumbar (or thoracic) disc space 104 againstthe background of a vertebral body. Note the expansile elastic polymernucleus 101, surrounded by an elastometric sheath, which is molded to(vulcanized) the inner surface of the outer titanium shells. Note thetitanium spikes 103. In FIG. 1A, it should be noted that the spikes areon four separate titanium plates (shells). Q1-Q4 which currently areadjacent to each other. This represents one of two leaflets of thedevice (rostral and caudal). Hence there are a total of eight moveabletitanium shells Q1-Q8. Upon ratcheting the height up with a screwdriver,the device 100 can be fine-tuned to the individual vertebral body height(FIG. 1). In FIG. 1B, an expansion device 102 causes the shells Q1, Q2to separate from shells Q3, Q4.

FIGS. 2A and 2B demonstrate ratcheting of the titanium shells Q1-Q4 toconform to the length of the lumbar/thoracic vertebral body 104.

Once the construct 100 has been fine-tuned to conform to the height andlength of the vertebral body 104, it can now be ratcheted to conform tothe width of the disc space and to be secured to the endplates 105. FIG.3A demonstrates the dorsal view of the construct 100 from the surgeon'sperspective, upon initial placement of the construct. Note the expansileartificial disc core 101, two leaflets of titanium shells Q1, Q2, Q5, Q6which are opposed to each other and the outer titanium spikes 103. Notethe three screws 111, 112, 113. One of three screws ratchets the heightof the implant (screw 111), another screw ratchets the length (screw112), and another screw ratchets the width (screw 1133). FIG. 3Billustrates the width-expanded construct 100 accommodating to individualdisc width, and titanium spike 103 endplate purchase.

FIGS. 4A-M illustrate the relationship of the screws to the internallyincorporated expansion device 102 or cylinder-spur-gear-spring (CSGS)system allowing expansion of the prosthesis in all three planes. Thereare a total of three screws. 111, 112, 113. Any one screw controls thehighly adjustable simultaneous movements of the appropriate titaniumshells with respect to one another on both rostral and caudal leaflets,in any one given dimension (x, y or z). This is accomplished byinternalizing and embedding within the titanium shells Q1-Q8 theexpansion device 102 or the gear mesh, a cylinder-spur-gear spring(CSGS) system. This system is designed such that turning screw 111adjusts the height of the prosthesis by moving the appropriate titaniumshells in the z axis. Turning screw 112 adjusts the length of theprosthesis by simultaneously moving the appropriate shells in the xaxis. Finally turning screw 113 leads to simultaneous expansion of theappropriate shells in the y axis. Turning screw 113 ensures the finallocking position of the prosthesis by engaging and incorporating theouter spikes into the opposing rostral and caudal vertebral endplates.

Referring now to FIG. 4A, a three dimension illustration of thelumbar/thoracic prosthesis 100 is provided, and it illustrates the threeaxes of motion (x,y, and z) vis-à-vis the interconnections between thesuperior/dorsal titanium shells (Q1, Q2, Q5, Q6) and theinferior/ventral shells (Q3, Q4, Q7, Q8), as well as the externalsurfaces of the titanium shells, as well as the external titanium spikes103. It should be noted that screw 111 adjusts height; screw 112 adjustslength, and screw 113 adjusts width, and that during surgery, height,length and width screws 111, 112, 113 are sequentially adjusted. Thetitanium shells of FIG. 4A include rostral leaflet superior shells Q1,Q2; rostral leaflet inferior shells Q3, Q4; caudal leaflet superiorshells Q5, Q6; and caudal leaflet inferior shells Q7, Q8.

Referring now to FIG. 4B, an illustration of lumbar/thoracic prosthesisheight and adjustment using screw 111 is provided. During a first stageof operation, screw 111 (height) is adjusted bycounter-clockwise/clockwise twisting. The amount of turning of thisscrew 111 determines the device's resting height (H). It should be notedthat in our Cartesian coordinate system, shell Q1 will always be fixedas a reference point (x=0,y=0,z=0). It should also be that noted thespace between the shells Q1-Q8 is to be filed with a core 101 asexplained in connections with embodiments I, II, III, IV, V. The core101 is taken out of FIGS. 4 a-4D to increase mechanical clarity.

Referring now to FIG. 4C, a three-dimensional illustration of thelumbar/thoracic prothesis 100 is provided. The length (L) is adjustedwith screw 112. During the second stage of operation, screw 112 (length)is adjusted by counter-clockwise/clockwise twisting. The amount ofturning of screw 112 determines the device's final resting length.

Referring now to FIG. 4D, a three-dimensional illustration oflumbar/thoracic prosthesis 100 is provided. The width (W) is adjustedscrew 113. During the third stage of operation, screw 113 (width) isadjusted by counter-clockwise/clockwise twisting. The amount of turningof screw 113 determines the device's final resting width (W). This stepis performed last, because the spikes 103 anchor into the bone.

Referring now to FIG. 4E, a side view of the expansion device 102controlled by the screws 111, 112, 113 is provided. The expansion device102 includes a plurality of components. Component S1X rotates about theY axis and moves along the Z axis. Component E2Z moves along the X axis.Component E2X rotates about the X axis, moves along the Y axis, and hasspring connection 114 at its midpoint. Component X1 rotates about the Xaxis. Component Y1 rotates about X, and moves along the Y axis.Component X2 rotates about the Y axis. Component Y2 rotates about X, andmoves along the Y axis. Component Z2 moves along the Z axis, and it hasa ball-socket joint 115 at its midpoint. Component E2Z moves along the Xaxis.

Referring now to FIG. 4F, a side view of the mechanical infrastructureof titanium shells Q1, Q3, Q5, Q7 is provided. Component Y2 rotatesabout X and moves along Y. Component Z1 moves along Z, has ball-socketjoint 115 at its midpoint. Component S1Z rotates about Z. Component S1Xrotates about X, and move along Z. Component S2Z rotates about Z.Component E1 is static with spring (not shown in diagram) connecting atmidpoint along the width axis. Component S2Y rotates about Y. ComponentX1 rotates abut X. Component Y1 rotates about X and moves along Y.Component X2 rotates about X.

Referring now to FIG. 4G, a dorsal view of the mechanical infrastructureof titanium shells Q1, Q2, Q5, Q6 is provided. S1Z rotates about Z.Component S2X rotates about X. Component E1 is static with a spring (notshown in diagram) connecting at midpoint along the width axis. ComponentS3X rotates about Y. Component Z1 moves along Z, and it has aball-socket joint 118 at its midpoint. Component X2 rotates about X.Component Y2 rotates about X and moves along Y. Component E2Y has ringsthat rotate about Y to force the structure to move along X. A coilspring is located at its midpoint. Component Z2 moves along Z and it hasa ball-socket joint 117 at its midpoint. E2Z: Moves along X. ComponentS1X rotates about Y and moves along Z. Component E1 is static withspring (not shown in diagram) connecting at midpoint along the widthaxis. Component S3Z rotates about Z. Component S2Z rotates about Z.

Referring now to FIG. 4H, a side view of the rostral titanium shells Q1,Q2, Q3, Q4 and the mechanical infrastructure is provided. Component S1Zrotates about Z. Component S2Z rotates about Z. Component S3Z rotatesabout Z. Component E1 is static with a spring (not shown in diagram)connecting at the midpoint along the width axis. Component E2Z movesalong X. Component Y2 rotates about X and moves along Y. Component X1rotates about X. Component Z2 move along Z. Component S1X rotates aboutX and moves along Z. Component Z1 moves along Z. Component S3Y rotatesabout Y. Component S2Y rotates about Y.

Referring now to FIG. 41, an axial view of caudal titanium shells Q5,Q6, Q7, Q8 and the mechanical infrastructure is provided. Component E2Zrotates about Y and moves along X. Component Z2 moves along Z. ComponentZ1 moves along Z. Component E1 is static with a spring (not shown indiagram) connecting at the midpoint along the width axis. Component S3Zrotates about Z. Component S2Z rotates about Z. Component S1Z rotatesabout Z. Component S1X rotates about X and moves along Z. S2Y rotatesabout Y. S3Y rotates about Y. Component D1 is satic. Component Z1 movesalong Z. Component Y2 rotates about X and moves along Y. Component Z2moves along Z. Component X2 rotates about X and moves along Y.

Referring now to FIG. 4J, a ventral view of titanium shells Q3, Q4, Q7,Q8 and the mechanical infrastructure is provided. Component X1 rotatesabout X. Component Z1 moves along Z. Component E2Y has rings that rotateabout Y to force the structure to move along X. A coil spring is locatedat its midpoint. Component X2 rotates about X. Component Y1 rotatesabout X and moves along Y. Component Z2 moves along Z. Component E1 isstatic with a spring (not shown in diagram) connecting at the midpointalong the width axis. Component S3Y rotates about Y. Component S2Yrotates about Y.

Referring now to FIG. 4K, the mechnaical infrastructre and heightadjustment components S1X, E2, Z2, E1, S1Z, Z1, Z2 are illustrated. InFIG. 4K(1), which provideds an overview of height adjustment system. Q3,Q4, Q7, Q8 are attached or linked to bottom pins as shown. Shells Q4 andQ8 are linked or connected to component Z2. Shells Q3 and Q7 are linkedor connected to component Z1. FIG. 4K(2), shows how twisting ofcomponent S1Z (by external screw driver) about Z translates to atwisting of component S1X about X (via miter gears 121). Component S1Zis twisted by an external screw driver. Rotation of component S1Z causesrotation of component S1X by way of miter gears 121. In FIG. 4K (3),component S1X is held in space by components E1, E2, yet is allowed totwist about, interacting with the racks on component Z1 and component Z2up or down along Z. Component S1X is held in space by a ring (thatallows it to twist however) on both ends that are fixed to E1 or E2(also by ring). Component Z1 is an upside-down letter-U shape that risesor lowers through holes in component E1. Component Z1 (and component Z2)has a rack on the left side of the U, as shown, to accommodate thecomplementary spurs on component S1X (in two locations). Since componentS1X is held in place by component E2 (which is relatively static),component Z1 must move up (or down) when component S1X is twisted.Components E1, E2 are spring connected in their respective midpointsalong the y(width) axis to allow for the Q1-Q2-Q3-Q4 complex to havethree degrees of freedom with respect to the Q5-Q6-Q7-Q8 complex.Components Z1 and Z2 have ball-socket joints along their y(width)midpoints for this same reason. Components Z1, Z2 use ball socketsrather than aspring-coil in order to allow for uniform z-directionmotion.

Referring now to FIG. 4L, the mechanical infrasructure length adjustmentcomponents E2, E1, S2Z, 2Y, X1, X2 are illustrated. In FIG. 4L(1), anoverview is provided of the length adjustment mechanism. Shells Q2, Q4,Q6, Q8 are attached or linked to component E2. In FIG. 4L(2), componentS2Z turns S2Y by miter gear (component S2Z is turned by an outsidescrew-driver). Component S2Z is twisted by an external screw driver.Rotation of component S2Z causes rotation of component S2Y by way of amiter gear. In FIG. 4L(3), component S2Y turns components X1, X2 by abevel gear. Component S2Y interacts with component X1 through a bevelgear mechanism. Rotation of component S2Y causes rotation of componentX1. In FIG. 4L(4), components X1 and X2 are threaded at the shown ends;their twisting caues the bevels surrounding E2 to move along thethreading (in X). Components X1 and X2 have threaded sections at theirends, as shown, which when twisted force component E2 to move along theX-axis. Component E2 does not rotate at all, but has two threaded ringsthat are allowed to rotate in place in order to move component E2 alongcomponents X1, X2.

Referring now to FIG. 4M, the mechanical infrastructure and adjustmentomponents E2, E1, S3Z, S3Y, Y1, Y2 are illustrated. In FIG. 4M(1), anoverview of the widh adjustment mechanism is provided. Shells Q5, Q6 areattached or linked to Y1. Shells Q7, Q8 are attached or linked tocomponent Y2. In FIG. 4M(2), the twisting of component S3Z by a screwdriver turns component S3Y by a miter gear. Component S3Z is twisted byan external screw driver. Rotation of component S3Z causes rotation ofcomponent S3Y by way of a miter gear. In FIG. 4M(3), component S3Y isshown threaded at the end that touches component Y1 and component T2.Components Y1 and Y2 are spirally threaded in opposing directions sothat both move in parallel along Y, either back or forth. Component Y1has two intermediate spured sections, one corresponding toacomplementary rack on component E1, and the other to a complementaryrack on component E2. Likewise, component Y2 has two spured sections.Both components Y1 and Y2 are beveled at their ends, as shown—inopposing diretions—one right-handed, the other left-handed. ComponentS3Y's rotation causes rotation in components Y1 and Y2, and therebytheir parallel movements along the double racked components E1 (and E2).

The present invention depends on an expansile disc core 101 that ismolded to the titanium shells (Embodiment I). Rubber, silicon, orpolyurethane variants are potential candidates for the core. Becausethere is already well-documented safe experience with elasticpolyurethane, this would be the most likely candidate. One skilled inthe art would need to select the most appropriate synthetic core, whichhas the physico-chemical properties of expansion upon release ofpressure, while still maintaining elastic resilience

Depending on the feasibility of finding and adapting a core with suchproperties, FIGS. 5A and 5B illustrate a second alternative embodiment(Embodiment II). FIG. 5A illustrates the first three stages of fillingthe device with an elastometric material, and FIG. 5B illustrates thefinal two stages. This design consists of the same boomerang shapedbi-leaflet with a total of eight ratchetable titanium shells Q1-Q8 in x,y and z planes. An expandable elastometric sheath 109 is molded to theshells, and can enlarge and conform to the disc space. Within thissheath is a coil 130 with pores (micro-catheter) attached to a port 131.Once the titanium shells Q1-Q8 are fine tuned to the height and lengthof the vertebral body, and the width fine tuned to the disc space,liquefied material can be injected into this port 131 from a source 132filling the elastometric balloon 109 until it fills the disc space andconforms to its geometry, as illustrated in FIG. 5B. It then cures(gels) permanently. This material could include polycarbonateurethane,polyurethane, polyvinyl alcohol, protein hydrogel, or any other materialthat one skilled in the art might select. The previous safe employmentof protein hydrogel and polyurethane in nucleus disc cores makes thesematerials the most likely candidates. The appropriate selection of coreswith specific chemico-physical properties is a significant designchoice.

FIGS. 6A, 6B and 6C illustrate a third alternative embodiment(Embodiment III). This embodiment is an expansile, custom-fit,mechanical metal on metal, ball on trough design (FIG. 6A). It consistsof two leaflets, rostral and caudal, 140 and 141. Each leaflet 140, 141in turn consists of three shells; 1) An inner stainless steel shell 142with a trough on the rostral leaflet, or with a protruding steel ball143 on the caudal leaflet, 2) An intermediate thin titanium plate 144 or145 which is molded to the outer surface of the stainless steel shells142, 143, and to the inner surface of the outer moveable titanium shellsQ1-Q8, and 3) Outer titanium shells Q1-Q8, four on each leaflet, whichwhen ratcheted glide over the intermediate titanium plates 144, 145allowing expansion of prosthetic height and length to conform i.e.custom fit to the individual vertebral endplate.

FIG. 6B(1) illustrates an axial composite view of the lumbar/thoracicmetal on metal, ball on trough prosthesis 100. It illustrates thehorizontal and vertical movements of the four titanium shells Q1-Q4 perleaflet expanding in height and length conforming to the particularvertebral body dimensions.

FIGS. 6B(1)-6B(3) illustrate different positions of the inner and outersurfaces of each of the separate three shells per leaflet, whichmechanically allow expansion of the implant in x, y, and z dimensionswhile maintaining a static relationship between the metal on metal balland trough. FIG. 6C(1) illustrates the outer surface of the outertitanium shells Q1-Q4. It has spikes 103 to engage the vertebralendplates, with four moveable shells as mentioned in the two otherdesigns above. FIG. 6C(2) illustrates the inner surface of the outertitanium shells Q1-Q4. It has both horizontal and vertical barelevations which fit into horizontal and vertical grooves 150, 151 ofthe outer surface of the intermediate titanium shells 144, 145. This isthe mechanism, which allows height and length prosthesis extension. Alsonote the cross section of four ratchetable bars 152 which extend fromthe intermediate titanium shell 144 to the outer surface of the innerstainless steel shell 142 allowing expansion of prosthetic disc width,while maintaining static contact between the inner surfaces of thestainless steel ball and trough.

FIG. 6C(4), illustrates the inner surface 153 of the intermediatetitanium shell 144. This is molded to the outer surface of the innerstainless steel ball and trough shells 142, 143. Also note thecross-section of the four width expansion bars 152.

FIGS. 6C(5) and FIG. 6C(6) illustrates the inner surfaces of the innerstainless steel shells 142, 143. The rostral leaflet has a depression154, i.e. a trough, serving as a socket for the steel ball 155 of theopposing leaflet. FIG. 6C(7) illustrates the outer surface of the innerstainless steel shells 142, 143. This is molded to the inner surface ofthe intermediate titanium shell 144. Also note the cross-section ofratchetable bars 152 allowing width expansion.

FIGS. 7A(1)-7A(2) illustrate a fourth alternative embodiment of thelumbar/thoracic design (Embodiment IV). This embodiment is an expansile,custom-fit, mechanical metal on metal, biconvex ultrahigh molecularweight polyethylene (UHMWPE) design. It consists of two leaflets 161,162, rostral and caudal. Each leaflet in turn consists of threeshells; 1) An inner UHMWPE convex shell 163, 2) An intermediate thintitanium plate 164 which is molded to the outer surface of the UHMWPEshell 163, and to the inner surface of the outer moveable titaniumshells Q1-Q8, and 3) Outer titanium shells Q1-Q8, four on each leafletwhich when ratcheted glide over the intermediate titanium plate 164allowing expansion of the prosthetic height and length to conform, i.e.custom fit to the individual vertebral endplate. FIG. 7A(2) illustratesthe width adjustment of the fourth alternative embodiment.

FIGS. 7B(1)-7B(3) illustrate an axial composite view of thelumbar/thoracic metal on metal, biconvex UHMWPE prosthesis. Itillustrates the horizontal and vertical movements of the four titaniumshells Q1-Q4 of one leaflet expanding in height and length conforming tothe particular vertebral body dimensions.

FIGS. 7C(1) and 7C(2) illustrate the axial views of the outer and innerUHMWPE biconvex shell 163 surfaces. The axial views of the outer andinner surfaces of the outer titanium shells Q1-Q8 are identical to thoseillustrated in FIGS. 6C(1) and 6C(2). The axial views of the outer andinner surfaces of the intermediate titanium shell is identical to thatillustrated in FIGS. 6C(3) and 6C(4).

FIGS. 8A and 8B illustrate a fifth alternative embodiment of the lumbar/thoracic disc (Embodiment V). This embodiment is an expansile, customfit, mechanical metal on metal, monoconvex UHMWPE design. It consists oftwo leaflets 171, 172, rostral and caudal. The rostral leaflet consistsof two shells; 1) an inner thin titanium shell 173 which is molded tothe inner surface of the 2) outer titanium shells Q1-Q4. The caudalleaflet has three shells; 1) An inner monoconvex UHMWPE shell 174, 2) Anintermediate thin titanium plate 175 which is molded (vulcanized) to theouter surface of the UHMWPE shell and to the inner surface of the outermoveable titanium shells Q1-Q4, and 3) Outer titanium shells Q1-Q8, fouron each leaflet, which when ratcheted glide over the intermediatetitanium plates 173, 174 allowing expansion of the prosthetic height andlength to conform, i.e. custom-fit to the individual vertebral endplate.The composite axial view of the total lumbar/thoracic metal on metal,monoconvex UHMWPE disc (Embodiment V) is identical to that illustratedin FIGS. 7B(1)-7B(3) (UHMWPE biconvex embodiment, IV). Thecross-sectional axial views of the outer and inner surfaces of the outertitanium shells for both rostral and caudal leaflets (Embodiment V) isidentical to that illustrated in FIGS. 6C(1) and 6C(2). The axial viewsof the outer and inner surfaces of the intermediate titanium shell ofboth rostral and caudal leaflets for Embodiment V is identical to thatillustrated in FIGS. 6C(3) and FIG. 6C(4). The axial views of the innerand outer surfaces of the monoconvex UHMWPE shell of the caudal leafletare identical to FIGS. 7C(1) and 7C(2). There is no equivalent UHMWPEshell on the rostral leaflet.

FIG. 9A illustrates a total Lumbar/Thoracic prosthetic disc 200, whichexpands in two instead of three dimensions. The prototype used toillustrate this design is a variant of the psedoannulus threedimensional designs employed in embodiments I-V. In this embodiment (VI)there are a total of four titanium shells Q′1-Q′4. There are two dorsalshells Q′1, Q′2 (rostral and ventral), and two caudal (rostral andventral) shells Q′3, Q′4. There is a single widened bar 220 attachingthe dorsal and ventral shells Q′1-Q′4 which expands the height byratcheting two screws 221 for either rostral or caudal height control.

FIGS. 9B(1) and 9B(2) illustrate the dorsal surgeon's view. Note thecentral width bar 224 which connects the rostral and caudal titaniumshells Q′1-Q′4 dorsally and ventrally. Ratcheting the central screw 225expands the dorsal width driving the dorsal rostral and caudal shelltitanium spikes 203 into the vertebral bodies. Ratcheting a ventralcentral width screw (not shown) widens the ventral rostral and caudalshells Q′3, Q′4 leading to engagement of spikes 203 into the bone. Thisscrew can be accessed endoscopically as will be described below.

FIG. 9C(1) illustrates an oblique view of the rostral and caudal shellsQ′1 and Q′2 and the width expansion bar 224 and ratchet screw 225. FIG.9C(2) illustrates an oblique view of the rostral and caudal shells Q′3and Q′4 and the width expansion bar 228 and ratchet screw 229.

FIG. 9D(1)-9D(3) illustrates an enlargement of the width widening bar224. It consists of an inner bar 231 with corrugations, which is incontact with inner grooves of the outer bar 232. By ratcheting thescrews 233, 234 in the clockwise direction, width expansion is achieved.By ratcheting the screws 233, 234 counter clockwise, width contractionis achieved. Prosthesis width expansion allows incorporation of thespikes 203 into the bone. Once the spikes have engaged the bone toachieve maximal expansion, screws 233, 234 can now be turned counterclockwise. This will lead to the contraction of the inner width bar 231within the outer width bar 232, enabling the removal of these bars fromthe construct. Now that the spikes 203 have engaged the bone, removal ofthe bars are important for allowing complete and uninhibited flexibilityof the prosthesis in this most important dimension.

FIG. 9E illustrates the axial view of the inner surfaces of the dorsaland ventral titanium shells Q′1 and Q′3 revealing the indented grooves239 into which the width bars 224, 228 is inserted, and expanded. Whenthe width bars 224, 228 are contracted, the bars fall away from thesegrooves 239 facilitating their removal.

This two-dimensional pseudo annulus variant (embodiment VI) can becombined with the same cores described for embodiments I, I, III, IV andV. Thus the cores used in embodiments I-V can be adapted and combinedwith a pseudo annulus which can expand in two or three dimensions. Tocompensate for the lack of length expansion of the two-dimensionaldesign, it would become necessary to design this variant with theappropriate range of differing length options.

FIG. 10A 1 illustrates a perspective of a total lumbar/thoracicprosthetic disc pseudo annulus 1000 (Embodiment VII) which expands intwo dimensions. The prosthetic disc 1000 includes four shells 1111,1112, 1113, 1114, and a plurality of spikes 1115. FIG. 10A 2 illustratesa simplified perspective view of the prosthetic disc 1000 and a pair ofjackscrew width expansion mechanisms 1022. Screws 1005, 1006 control thejackscrews 1021, 1022 respectively. FIG. 10A 3 is a perspective viewthat illustrates the jackscrews 1021, 1022 and two fixed-screw heightexpansion mechanisms 1023, 1024 which are controlled by screws 1001,1002, 1003, 1004. This Embodiment VII can also be combined with eitherof the cores of embodiments I, II, IIl, IV or V.

FIG. 10B illustrates a side view of the prosthetic disc 1000 thatsequential turning of screws 1001, 1002, 1003, 1004 leads to heightexpansion of the rostral and caudal shells 1111, 112 by widening thedistance between their superior and inferior shells.

FIG. 10C illustrates that turning screws 1005, 1006 leads to widthexpansion of the prosthesis 1000 by widening the distance between therostral and caudal superior and inferior shells 1111-1114.

FIG. 10D illustrates an enlarged simplified perspective view of thejackscrew width expansion mechanisms 1021 and 1022.

FIG. 10E illustrates that once maximum width expansion of prostheticdisc 1000 and purchasing of spikes have been achieved, the jackscrews1021 and 1022 can be removed by counter turning screws 1005 and 1006.Removal of these screws 1005, 1006 allows unconstrained or semiconstrained motion of the prosthetic device 1000 depending on which coreis selected to be inserted into this pseudo annulus embodiment.

FIGS. 11A1-11A6 illustrate the basic jackscrew 1021 opening and closingmechanism of embodiment VII. IIlustrated is the geometric conformationthe jackscrew 1021 assumes enabling expansion of the rostral and caudalshells 1111-1114, and the conformation it assumes allowing its removal.As illustrated in FIG. 11A 3, the more horizontally aligned the fourarms 1031-1034 of the jackscrew 1021 are the greater the expansion. Asillustrated in FIG. 11A 5, the more vertically oriented the four arms1031-1034 of the jackscrew 1021 are the greater the contraction.

FIG. 11B 1-11B6 illustrate the mechanism of mechanical opening andclosing of the jackscrew 1021 (embodiment VII). A straight screw 1005 isattached to the superior and inferior central apices of the jackscrew1021. Turning the screw 1005 counterclockwise leads to horizontallyoriented expansion/lengthening of the jackscrew 1021 arms which areattached to the titanium shells 1111-1114 achieving device expansion.Turning the straight screw 1005 clockwise leads to vertically orientedcontraction/shortening of the jackscrew arms 1031-1034 allowing thejackscrew 1021 to be detached from the titanium shells 1111-1114 uponfinal engagement of the shells' titanium spikes.

FIG. 11C 1-11C6 illustrates a mechanism for sequential electricalopening and closing of the jackscrew 1021 employed in embodiment VII. Asillustrated in FIG. 11C 2, two partially insulated wires 1041, 1042(e.g. nitinol) are embedded into the jackscrew 1021. One verticallyoriented wire 1041 is attached to the superior and inferior jackscrewapices 1043, 1044. Another horizontally oriented wire 1042 is attachedto the rostral and caudal jackscrew apices 1045, 1046. When power isapplied to the vertical wire 1041 from the power supply 1050 byactivating the switch the four arms of the jackscrew 1021 contractachieving more horizontally oriented positions thereby expanding thedevice. When power is applied to the horizontal wire 1042, the four armsof the jackscrew 1021 achieve a more vertical position thereby leadingto contraction of the device. The jackscrew 1021 can then be removed asillustrated in FIG. 11C 6. The electrical jackscrew 1021 can becontrolled by an external power source 1050 making it wire controlled.Alternatively the power source can be enclosed in the jackscrew 1021itself making it a wireless device. If desirable the same electricaljackscrew mechanism 1021 may be employed for vertical height expansionof the embodiments as well.

FIGS. 11D1-11D6 illustrates a hybrid mechanical-electrical mechanism toexpand and contract the jackscrew 1021 of embodiment VII. This designemploys the placement of a vertical screw 1005 as well as a verticallyoriented insulated wire 1041 attached to the superior and inferiorapices of the jackscrew 1021. It also has a horizontally orientedinsulated wire 1042 attached to the rostral and caudal apices of thejackscrew 1021. The purpose of this design is to have a mechanicalbackup in the event of an electrical failure/malfunction. The power froma power supply 1050 applied can be external to the jackscrew 1021 makingit wire controlled, or it could be enclosed in the jackscrew 1021 makingit wireless controlled.

a. The Surgical Method

The surgical steps necessary to practice the present invention will nowbe described.

For posterior lumbar spine prosthetic implantation there are twoembodiments of the surgical approach: A) Classic microscopic open lumbarhemilaminotomy and discectomy, and B) Minimally invasive microendoscopichemilaminotomy and discectomy.

Classic Microscopic Open Hemilaminotomy/Discectomy (Approach A):

Step 1. After the adequate induction of general anesthesia, the patientis placed prone on a radiolucent Jackson table. The patient is preppedand draped and using x-ray or fluoroscopic guidance, the correct discspace is identified. The microscope is brought in for appropriatemagnification of the operative site. A routine hemilaminotomy isperformed as fully described elsewhere.

Step 2. A complete discectomy is performed, and the endplates arecuretted thereby preparing the disc space for prosthesis implantation.An endoscope can be employed to verify from a unilateral hemilaminotomya successful circumferential discectomy. FIG. 12A illustrates anendoscope variant of the present invention having an endoscope 301 and amonitor 302 that specifically looks into the disc space 104 (discoscope)to verify an adequate circumferential discectomy. FIG. 12B illustrates aspecifically lightweight design pituitary rongeur endoscopic 304attachment, which can also be used to assist in complete and adequatediscectomy for prosthesis implantation. A specifically designedright-angled screw ratcheter endoscopic attachment 305 can be used toaid in visualization and ratcheting of screws if partially hidden by thespinal cord orthecal sac as in FIG. 12C.

Step 3. The boomerang shaped artificial lumbar/thoracic disc, embodimentI, II, III, IV, V or VI is unilaterally inserted into the disc space bygently retracting the thecal sac and nerve root, and using a forceps ora similar specifically designed instrument to grab and secure thedevice. Once the edge of the boomerang is introduced into the discspace, it is then curvalinearly further inserted into the disc spaceunderneath the thecal sac and nerve root, aligning the horizontal axisof the prosthesis with the horizontal axis of the vertebral endplate.

Step 4. Once the construct is beneath the thecal sac, using livefluoroscopy, adjust (ratchet) the construct height (Screw 1) until theouter titanium shells conform to the individual vertebral endplateheight. Specifically designed screwdrivers, straight or right-angled, ofappropriate length and screw fittings are employed.

Step 5. Now again using live fluoroscopy adjust (ratchet) the length ofthe titanium shells until the prosthesis conforms to the desiredindividual length of the vertebral body (Screw 2). In embodiments VI andVII there are no length adjustments. Measurements of the length of thevertebral bodies will determine the selection of prefabricatedprostheses of different lengths.

Step 6. Now under direct microscopic or endoscopic visualization adjust(ratchet) the prosthesis width screw. As the width is expandedconforming to the precise disc width, the titanium outer spikes willengage, and then penetrate the bony endplates. Once total spike-bonepenetration has occurred with complete purchase of the spikes, theimplant is now safely secured in its position, and custom fit withrespect to all x, y and z planes. Final lateral and anterior-posteriorfluoroscopic images are then obtained to verify the precision fit.Verification of prosthetic purchase to the endplates can be performed bygrasping and testing the prosthesis with a forceps verifying lack ofmotion. For Embodiment VI, once width expansion has been achieved, andthe spikes 200 incorporated into the bone, the width bars 224, 228 areremoved by turning screws 225, 229 counter clockwise (see FIGS. 9C(1)and 9C(2)). For embodiment VII once width expansion has been achievedthe jackscrews are removed (see FIGS. 10E and FIGS. 11A, 11B, 11C AND11D)).

B) Posterior Lumbar Minimally Invasive Microendoscopic LumbarHemilaminotomy (Approach B).

Step 1. After the adequate induction of general anesthesia the patientis placed prone on a radiolucent Jackson table. The patient is preppedand draped. Then using fluoroscopic guidance a minimally invasivemicroendoscopic approach is used to gain access to the appropriate discspace as described in detail elsewhere. In brief, serial tubulardilators are sequentially placed in the dorsal musculature and fasciathrough which a working channel is created and an endoscope is docked onthe appropriate laminar landmark.

Step 2. Through the working channel a discectomy is performed. Theendoscope can be repositioned to verify complete discectomy.

Steps 3-6 are then performed identically to steps 3-6 mentioned above(Approach A; Posterior lumbar placement using an open classicalmicroscopic technique).

The steps for anterior implantation of lumbar/thoracic prostheticdevices, embodiments I, II, IIl, IV, V, VI or VII into the lumbar L4/5and L5/S1 disc interspaces will now be outlined.

Step 1. After the adequate induction of general anesthesia the patientis placed supine on the radiolucent Jackson table. The patient isprepped and draped. A General abdominal surgeon creates aninfraumbilical incision, and then using a retroperitoneal ortransperitoneal approach as described in detail elsewhere, the L4/5 orL5/S1 disc spaces are identified using fluoroscopic or x-ray guidance.

Step 2. The microscope is now brought in and a complete discectomy isperformed which can be verified under direct microscopic vision.

Step 3. The prosthetic disc, embodiment I, II, III, IV, V, VI or VII isplaced with forceps directly into the disc space with the horizontalaxis of the device aligned with the horizontal axis of the vertebralbody. The convex lower aspect of the device is placed above the ventralsurface of the thecal sac. The dorsal upper aspect of the prosthesiswith its ratcheting screws is in the surgeon's field.

Step 4. The prosthesis is secured with a forceps, and using fluoroscopicguidance, the prosthesis height is expanded to custom fit the vertebralendplate by ratcheting screw 1 with the appropriately designedscrewdriver.

Steps 5 and 6 are now identical to steps 5 and 6 used for posteriorlumbar placement (Approach A).

The surgical steps necessary to practice the present invention forposterior implantation of the lumbar/thoracic artificial disc,embodiment I, II, III, IV VI or VII into the thoracic disc interspacewill now be described.

Step 1. After the adequate induction of general anesthesia the patientis positioned prone on a radiolucent Jackson table. The patient isprepped and draped. Then utilizing fluoroscopic or x-ray guidance, thecorrect and relevant spinous processes and posterior elements areidentified. Then using a standard extracorporeal, transpedicularapproach, the rib head is removed and the pedicle drilled overlying theappropriate disc space as fully described in detail elsewhere.

Step 2. The microscope is now brought in for appropriate magnification.The discectomy is performed routinely. An endoscope can be employed toverify complete circumferential discectomy.

Step 3. The lumbar/thoracic prosthesis, embodiment I, II, III, IV, V, VIor Vllis introduced into the disc space using a forceps aligning thehorizontal axis of the device with the horizontal axis of the vertebralbody. The concave surface of the prosthesis is now placed severalmillimeters under the spinal cord. Specifically designed right-angledscrewdrivers, are introduced ventral to the cord, and custom fit theprosthesis to the vertebral endplate by ratcheting the length, heightand width of the prosthesis.

Steps 4-6 are now identical to steps 4-6 of the posterior lumbarsurgical approach A.

The surgical steps necessary to practice the present invention for theanterior implantation of artificial discs, embodiment I, II, III, IV, Vor VI into the thoracic spine will now be described.

Step 1. After the adequate induction of general anesthesia, the patientis positioned on a beanbag in the lateral position, with the right orleft side up depending on the side of the disc herniation. A thoracicsurgeon now performs a thoracotomy, the lung is deflated, and usingfluoroscopic or x-ray guidance, the appropriate disc space is identifiedand visualized as described in detail elsewhere.

Step 2. The microscope is now brought in and a discectomy is performedroutinely. Complete and adequate discectomy is confirmed under directvisualization.

Step 3. The lumbar/thoracic prosthesis, embodiment I, II, III, IV, V, VIor VII is placed with forceps directly into the disc space aligning thehorizontal axis of the device with the horizontal axis of the vertebralbody. The convex lower surface of the device is placed under the ventralsurface of the cord. The concave dorsal surface is facing the surgeonsuch that there is direct visualization of the ratchetable screws.

Steps 4-6 are now identical to steps 4-6 of the posterior lumbarplacement approach A.

FIGS. 13A(1)-13D(3) illustrate an alternative cervical disc embodimentor prosthetic disc 400 which includes a core similar to embodiments I,II, III, IV and V, and it is specifically configured for anteriorimplantation. These figures illustrate the axial views of this cervicaldisc alternative embodiment. They illustrate expansion of prostheticcervical disc height and length. For the cross-sectional axial views ofall outer and inner surfaces of the multiple shells, and for themechanical infrastructure (CSGS), and for the dorsal surgeons viewillustrating prosthetic width expansion refer to the correspondingfigures illustrating these views for lumbar/thoracic disc alternativeembodiments, embodiments I, II, III, IV and V (FIGS. 3, 4, 5B, 7A, and8). These views are virtually identical. Because the cervical spine isless rectangular than the lumbar or thoracic spine, and placement is viaan anterior approach, the prosthetic implant 400 takes on a moresquare/rectangular design (FIGS. 13A(1)-13D(3) as opposed to a boomerangbean-shaped design. The. two-dimensional expansile variant for cervicalembodiments I-V, i.e. embodiments VI and VII are identical to thatillustrated for the Thoracic-Lumbar prosthesis, except for therectangular design of the cervical titanium shells.

The surgical steps necessary to practice the present invention foranterior implantation of prosthetic discs, embodiment I, II, III, IV, V,VI or VII into the cervical spine will now be described.

Step 1. After the adequate induction of general anesthesia, the patientis positioned supine on the radiolucent Jackson table. An interscapularroll is placed and the patient's neck is prepped and draped. Ahorizontal incision is made overlying the appropriate disc interspacewith the aide of fluoroscopy or x-ray. The platysma is divided, theesophagus and trachea retracted, the anterior spine exposed, and theappropriate disc space verified radiographically as described in detailelsewhere.

Step 2. The microscope is brought in for appropriate magnification ofthe operative site. A complete discectomy is performed under directvisualization.

Step 3. The cervical prosthesis embodiment, embodiment I, II, III, IV, Vor VI is placed with a forceps directly into the disc space aligning thehorizontal axis of the device with the horizontal axis of the vertebralbody. The dorsal surface of the prosthesis with ratchetable screws isfacing the surgeon. The ventral surface of the prosthesis is above thecervical spinal cord.

Step 4. Once the prosthesis is in the disc space above the spinal cord,using fluoroscopic guidance screw 1 is rotated thereby ratcheting theouter titanium shells until they conform to the individual vertebralplate height.

Steps 5 and 6 are now identical to steps 5 and 6 of posterior placementof lumbar/thoracic artificial discs-approach A.

Because the current embodiment of cervical prosthetic discs lackanterior screw fixation, multi-level disc replacements can now beentertained. Furthermore with respect to all the lumbar, thoracic andcervical prosthetic disc embodiments surgically implanted via posterioror anterior approaches, it is unnecessary to have multiple sizes of eachprosthesis. For embodiments I-V one lumbar/thoracic prosthesis of eachof the five design embodiments can be custom fit for the individuallumbar or thoracic disc space. One cervical prosthesis of eachparticular design embodiment can be custom fit for the individualcervical disc space. For embodiments VI and VII only two or maximumthree length options can be chosen. The ease of placement diminishesoperating room time and decreases morbidity and mortality. This featureof Embodiments I II III IV, V, VI and VII is unique compared to allother designs to date.

The present invention may provide an effective and safe technique thatovercomes the problems associated with current techniques, and for mostdegenerative disc conditions it could replace pedicle screwinstrumentation and fusions.

1. A total artificial expansible disc, comprising: at least two pairs ofsubstantially parallel shells, that move in multiple directions definedby at least two axes, in order to occupy a space defined by vertebralendplates; an expansion device, that moves the pairs of shells inmultiple directions, having at least one jackscrew mechanism; and acore, disposed between the pairs of shells, that permits the vertebralendplates to move relative to one another.
 2. A total artificialexpansible disc according to claim 1 wherein the shells include aplurality of spikes that are embedded in the vertebral endplates.
 3. Atotal artificial expansible disc according to claim 1 wherein the coreis fabricated from an elastic material.
 4. A total artificial expansibledisc according to claim 1 wherein the core is fabricated from a materialselected from a group of materials comprising rubber, silicone, orpolyurethane.
 5. A total artificial expansible disc according to claim 1wherein the core includes an expandable elastomeric sheath that ismolded to the inner surfaces of the shells and that can expand tosubstantially fill the space between the shells.
 6. A total artificialexpansible disc according to claim 5 wherein a curable liquefiedmaterial is injected into the sheath causing it to expand.
 7. A totalartificial expansible disc according to claim 6 wherein the liquefiedmaterial is selected from a group of materials comprisingpolycarbonateurethane, polyurethane, polyvinyl alcohol, or proteinhydrogel.
 8. A total artificial expansible disc according to claim 6wherein the sheath includes a coil and a port.
 9. A total artificialexpansible disc according to claim 1 that further includes at least twoinner shells disposed near the moveable shells, the first inner shelldisposed near the outer moveable shells which form a rostral leaflet,and the second inner shell disposed near the outer moveable shells whichform a caudal leaflet; the first inner shell having a trough and thesecond inner shell having a protruding ball that cooperates with thetrough.
 10. A total artificial expansible disc according to claim 9 thatfurther includes intermediate plates disposed between the outer andinner shells.
 11. A total artificial expansible disc according to claim10 wherein the outer shells and the inner plates are made from titaniumand the inner shells are made from stainless steel.
 12. A totalartificial expansible disc according to claim 1 that further includes atleast two inner shells disposed near the moveable shells, the firstinner shell disposed near the outer moveable shells which form a rostralleaflet, and the second inner shell disposed near the outer moveableshells which form a caudal leaflet; the first inner shell having aconvex shape and the second inner shell having a convex shape.
 13. Atotal artificial expansible disc according to claim 12 that furtherincludes intermediate plates disposed between the outer and innershells.
 14. A total artificial expansible disc according to claim 10wherein the outer shells and the inner plates are made from titanium andthe inner shells are made from UHMWPE.
 15. A total artificial expansibledisc according to claim 1 that further includes at least two innershells disposed near the moveable shells, the first inner shell disposednear the outer moveable shells which form a rostral leaflet, and thesecond inner shell disposed near the outer moveable shells which form acaudal leaflet; the first inner shell having a substantially planarshape and the second inner shell having a convex shape.
 16. A totalartificial expansible disc according to claim 15 that further includesan intermediate plate disposed between the outer and inner shells of thecaudal leaflet.
 17. A total artificial expansible disc according toclaim 10 wherein the outer shells, the first inner shell and theintermediate plate are made from titanium, and the second inner convexshell is made from UHMWPE.
 18. A total artificial expansible discaccording to claim 1 wherein the moveable shells form a dorsal pairhaving rostral and caudal shells, and the moveable shells form a ventralpair having rostral and caudal shells; and wherein the dorsal pair andventral pair move apart.
 19. A total artificial expansible discaccording to claim 18 wherein the moveable shells form a rostral pairhaving dorsal and ventral shells, and the moveable shells form a caudalpair having dorsal and ventral shells; and wherein the rostral pair andcaudal pair move apart.
 20. A total artificial expansible disc accordingto claim 1 wherein the jackscrew mechanism includes a plurality of arms,and the jackscrew mechanism is activated by a screw disposed at apicesof the of the jackscrew arms.
 21. A total artificial expansible discaccording to claim 20 wherein the jackscrew mechanism includes aplurality of arms, and the jackscrew mechanism is activated by either atleast one contraction wire disposed at apices of the jackscrew arms or ascrew disposed at apices of the of the jackscrew arms.
 22. A totalartificial expansible disc according to claim 1 wherein the jackscrewmechanism includes a plurality of arms, and the jackscrew mechanism isactivated by at least one contraction wire disposed at apices of thejackscrew arms.
 23. A total artificial expansible disc according toclaim 22 wherein the contraction wire is responsive to a power supplydisposed externally of the jackscrew mechanism.
 24. A total artificialexpansible disc according to claim 22 wherein the contraction wire isresponsive to a power supply disposed internally of the jackscrewmechanism.
 25. A total artificial expansible disc according to claim 22wherein jackscrew included two contraction wires one being disposed in asubstantially vertical direction and the other being disposed insubstantially a horizontal direction.
 26. A total artificial expansibledisc according to claim 1 wherein the moveable shells form a boomerangshape.